Concrete used for building of structures comprises cement, water, aggregates and the like, and is of such a nature that it hardens by hydration reaction. Hardened concrete is susceptible to cracking due to the action of stress, and to volume changes caused by temperature variations, drying, or the like. When cracking is produced, water readily infiltrates the concrete, resulting in water leakage and other problems while also leading to reduced structural durability and impaired aesthetic quality. Water leakage due to cracking is also a problem with underground structures, for example, in which cases cost is amplified because of the difficulty of repair operations for the cracking. Conventional measures have included reparation by injection of fillers after cracking has formed, or waterproofing or water-blocking the concrete so that the structures are not affected even when cracking has formed.
Measures such as reparation, waterproofing and water-blocking, however, necessarily increase cost and potentially lengthen the construction period for structure building, and are therefore preferably avoided when possible. This has led to development of “self-healing concrete” that can undergo auto-repair even when cracking has been formed (see Patent documents 1 and 2, for example). Such concrete has a property allowing it to repair its own cracking, and can maintain water-blocking performance and durability even without the reparations or waterproofing and water-blocking treatment described above.    [Patent document 1] Japanese Patent Publication No. 3658568    [Patent document 2] Japanese Unexamined Patent Application Publication No. 2005-239482